密闭式吸痰法对使用呼气末正压通气的危重症患者呼吸循环功能的影响

目的 探讨密闭式吸痰法对使用呼气末正压通气(PEEP)的危重症患者动脉血气、呼吸力学和血液动力学的影响.方法 将92例使用PEEP的危重症患者随机分为采用开放式吸痰法(OS)和密闭式吸痰法(CS),通过动脉血气分析、呼吸机参数和PICCO机参数监测2组患者吸痰前1min及吸痰后1min、5min、15min动脉血气、呼吸力学及血液动力学的变化情况.结果 2组患者在吸痰后即刻动脉血氧分压和动脉血氧饱和度均下降,OS组直到吸痰后15min仍低于吸痰前基线水平;而有创收缩压、有创平均动脉压均升高,吸痰后15minOS组仍高于吸痰前基线水平,CS组高于吸痰前基线水平但无差异(p＞0.05);而有创舒张压(DBP)与吸痰前比较2组均无差异(p＞0.05).OS组在吸痰后肺静态顺应性、心脏指数均降低,持续到吸痰后15min仍低于吸痰前基线水平;气道峰压、平台压、平均气道压均升高,持续到吸痰后15min仍显著高于吸痰前基线水平(p＜0.05).CS组在吸痰后持续到吸痰后15min与吸痰前基线水平差异无统计学意义(p＞0.05).结论 密闭式吸痰过程中可以保持持续通气,维持PEEP,避免或减少肺泡萎陷,维持吸痰前后呼吸循环的相对稳定性,是使用正压通气的危重症患者安全有效的吸痰方法.     

两种吸痰方式预防心胸外科术后机械通气患者呼吸道感染的效果

目的 探讨密闭式吸痰和开放式吸痰两种方式对预防心胸外科术后机械通气患者呼吸道感染的效果.方法 2009年9月-2010年8月,将86例心胸外科术后机械通气患者随机分为两组,试验组应用密闭式吸痰法,对照组采用开放式吸痰法.观察两组患者术后机械通气治疗即刻及至拔出气管插管后48 h内每日痰培养结果、每4小时监测一次体温、血...     

密闭式吸痰对艾滋病机械通气患者血氧改变及机会性感染的研究

目的:探讨密闭式吸痰与开放式吸痰对艾滋病人工机械通气患者血氧饱和度及并发机会性感染的影响.方法:将56例使用PEEP模式机械通气的艾滋病患者随机分为观察组和对照组各28例,分别采用密闭式吸痰和开放式吸痰,观察两组患者吸痰前后血氧改变情况以及机械通气3d后机会性感染发生情况.结果:对照组吸痰1 min与吸痰前比较,患者的脉搏血氧饱和度(SpO2)无明显下降(P＞0.05),吸痰2 min后SpO2值与吸痰前比较下降明显(P＜0.05);而观察组在吸痰1、2 min SpO2值与吸痰前比较无统计学意义(P＞0.05);吸痰超过3min时两组SpO2值均明显降低,与吸痰前比较均有统计学意义(P＜0.01).对照组在机械通气治疗3d后71.43％的艾滋病患者并发多种机会性感染,而观察组在治疗3d后仅21.43％的艾滋病患者并发机会性感染,两组比较有统计学意义(P＜0.01).结论:密闭式吸痰法在机械通气的艾滋病人群中应用能有效避免因脱机吸痰导致的Sp02下降,并降低机会性感染的发生率,节约护理成本,避免交叉感染,是艾滋病机械通气患者的最佳吸痰法.     

吸痰方式对急性呼吸窘迫综合征呼吸力学影响的实验研究

目的研究更适宜急性呼吸窘迫综合征(ARDS)机械通气犬气管内吸痰的方式。方法采用静脉注射油酸制备犬ARDS模型;每只犬随机选择使用开放式气管内吸痰(OS)和密闭式气管内吸痰(CS)2种吸痰方式。于吸痰前后记录呼吸力学监测指标的数据。结果OS和CS后,犬吸气峰压(Ppeak)、平台压(Pplat)、平均气道压力(Pmean)与吸痰前比较均明显上升(P<0.05);OS后肺动态顺应性(CD)、静态顺应性(CS)显著下降(P<0.05)。结论OS、CS均可影响气道压力;OS后降低肺顺应性。本研究提示我们,在护理工作中,应加强吸痰前后气道压力等监测;对ARDS机械通气犬吸痰时选择CS方式更适宜和安全。     

ICU机械通气患者两种吸痰方法的比较

目的探讨机械通气患者有效的吸痰方法。方法将ICU行机械通气的96例患者随机分为观察组和对照组,观察组采用改进吸痰法,对照组采用常规吸痰法。观察吸痰前后心率、血压、潮气量、气道压力、氧分压、血氧饱和度、肺部相关并发症等情况。结果观察组吸痰前后除心率、血压、潮气量外,气道压力、氧分压、血氧饱和度、肺部相关并发症等均差异有显著意义(P<0.05)。结论在对机械通气患者进行吸痰时,使用吸痰→湿化→扩肺→吸痰→扩肺或者吸痰→扩肺的方法,可以提高吸痰效果,减少肺部相关并发症。     

不同吸痰方式对急性呼吸窘迫综合征血流动力学影响的实验研究

目的研究更适宜急性呼吸窘迫综合征(ARDS)机械通气气管内吸痰的方式。方法采用静脉注射油酸制备动物ARDS模型;每只犬随机选择使用开放式气管内吸痰(OS)和密闭式气管内吸痰(CS)2种吸痰方式。于吸痰前后记录血流动力学等监测指标的数据。结果OS和CS后,犬平均肺动脉压(MPAP)与吸痰前比较均明显升高(P<0.05);OS后平均动脉压(MAP)显著升高(P<0.05)。结论OS、CS均可影响血流动力学的稳定。本研究提示,在护理工作中,对ARDS机械通气者应重视吸痰引起的继发性损害,加强吸痰前后血流动力学等监测。     

密闭式吸痰器与一次性吸痰管吸痰效果的比较

目的比较密闭式吸痰器与一次性吸痰管的吸痰效果。方法采用方便取样法,选择北京市某三级甲等医院心脏外科ICU行心脏外科手术的术后患者100例,随机分为实验组和对照组各50例。实验组使用密闭式吸痰器,对照组使用一次性吸痰管,由护士随机对两组患者进行吸痰操作,从术后机械通气时间、术后机械通气期间的平均每次吸痰时间、平均吸痰间隔时间、氧分压和脉氧饱和度均值、经人工气道吸痰费用进行分析对比。结果两组患者术后机械通气时间差异无统计学意义（P〉0．05）;实验组平均每次吸痰时间、平均吸痰间隔时间均少于对照组,差异有统计学意义（P〈0．05）;实验组氧分压和脉氧饱和度均值、经人工气道吸痰费用均高于对照组,差异有统计学意义（P〈0．01）。结论密闭式吸痰器的临床吸痰效果优于一次性吸痰管,增加了患者术后机械通气期间的氧储备,提高了护士吸痰操作的主动性,减轻了护理工作量,但费用较高。     

不同吸痰方式对重型颅脑损伤患者颅内压水平影响的效果分析

目的探讨不同吸痰方式对重型颅脑损伤患者的应用效果。方法选择我院2012年1月~2015年8月收治重型颅脑损伤并行人工气道机械通气的患者80例,按入院顺序进行编号,并根据随机数字法分为开放式吸痰和闭合式吸痰两组,每组各40人。监测吸痰前后患者颅内压、心率、痰鸣音及血氧饱和度的变化情况。结果开放式吸痰组颅内压升高幅度大于闭合式吸痰组(P0.05),开放式吸痰组比闭合式吸痰组更易发生低氧血症(P0.05),而患者的痰鸣音及心率影响比较无显著性差异(P0.05)。结论重型颅脑损伤机械通气患者密闭式吸痰的效果优于开放式吸痰,值得临床推广应用。     

吸痰方式对急性呼吸窘迫综合征呼吸力学影响的实验研究

目的研究更适宜急性呼吸窘迫综合征(ARDS)机械通气犬气管内吸痰的方式.方法采用静脉注射油酸制备犬ARDS模型;每只犬随机选择使用开放式气管内吸痰(OS)和密闭式气管内吸痰(CS)2种吸痰方式.于吸痰前后记录呼吸力学监测指标的数据.结果OS和CS后,犬吸气峰压(Ppeak)、平台压(Pplat)、平均气道压力(Pmean)与吸痰前比较均明显上升(P＜0.05);OS后肺动态顺应性(CD)、静态顺应性(Cs)显著下降(P＜0.05).结论OS、CS均可影响气道压力;OS后降低肺顺应性.本研究提示我们,在护理工作中,应加强吸痰前后气道压力等监测;对ARDS机械通气犬吸痰时选择CS方式更适宜和安全.     

不同气管内吸痰方式对呼吸窘迫综合征机械通气患者呼吸功能的影响

目的 探讨开放式吸痰与密闭式吸痰对呼吸窘迫综合征机械通气患者动脉血气(PaO<,2>,PaCO<,2>,SaO<,2>)的影响.方法 将78例使用ARDS机械通气患者随机分为对照组与观察组各39例,对照组采用开放式吸痰,观察组采用密闭式吸痰,两组患者吸痰前及吸痰后即刻、吸痰后2 min、5 min、10 min动脉血气...     

Clinical review: Positive end-expiratory pressure and cardiac output

In patients with acute lung injury, high levels of positive end-expiratory pressure (PEEP) may be necessary to maintain or restore oxygenation, despite the fact that 'aggressive' mechanical ventilation can markedly affect cardiac function in a complex and often unpredictable fashion. As heart rate usually does not change with PEEP, the entire fall in cardiac output is a consequence of a reduction in left ventricular stroke volume (SV). PEEP-induced changes in cardiac output are analyzed, therefore, in terms of changes in SV and its determinants (preload, afterload, contractility and ventricular compliance). Mechanical ventilation with PEEP, like any other active or passive ventilatory maneuver, primarily affects cardiac function by changing lung volume and intrathoracic pressure. In order to describe the direct cardiocirculatory consequences of respiratory failure necessitating mechanical ventilation and PEEP, this review will focus on the effects of changes in lung volume, factors controlling venous return, the diastolic interactions between the ventricles and the effects of intrathoracic pressure on cardiac function, specifically left ventricular function. Finally, the hemodynamic consequences of PEEP in patients with heart failure, chronic obstructive pulmonary disease and acute respiratory distress syndrome are discussed.     

呼气末正压通气对伴有低血容量趋势行机械通气患者血流动力学的影响

目的探讨呼气末正压（PEEP）对低血容量趋势患者行机械通气时血流动力学的影响。 方法选择20例伴有低血容量趋势需行机械通气的患者作为研究对象。所有患者均在基础呼吸模式上分别加用PEEP 0、5、10、15 cmH₂O,每次持续约30 min。记录所有患者的心率、平均动脉压（MAP）、肺动脉嵌压（PAWP）、每搏指数（SVI）、心排血量（CO）、心指数及体循环血管阻力指数（SVRI）等血流动力学指标,中心静脉压（CVP）、髂总静脉压（CIVP）及ΔCVP等静脉回流梯度指标,吸气峰压（PIP）、气道阻力（RAW）、用吸气暂停键测出平台压（Pplat）、气道平均压力（Pmean）及肺循环血管阻力指数（PVRI）等呼吸力学指标。 结果随着PEEP水平的增加,患者心率、PAWP及SVRI均显著增加,而MAP、CO、心指数及SVI则逐渐下降（F = 20.311、15.100、32.915、15.100、198.635、435.100、17.000,P均< 0.001）,且CO于PEEP为5 cmH₂O时与PEEP为0 cmH₂O时比较,已经出现显著降低[（5.31 ± 0.11）L / min vs.（5.46 ± 0.24）L / min];患者的CVP、CIVP的水平逐渐升高,而ΔCVP逐渐下降（F = 47.879、27.578、21.393,P均< 0.001）;患者的PIP、Pplat、Pmean、PVRI水平均逐渐升高,且PEEP为15 cmH₂O时达最高（F = 67.152、74.025、818.208、31.141,P均< 0.001）,而RAW在不同PEEP间比较差异无统计学意义（F = 2.082,P = 0.131）。 结论对有低容量趋势行机械通气的患者,当PEEP ≥ 5 cmH₂O即出现CO明显下降,因此对于有低容量趋势患者尽量使用最小PEEP来达到治疗目的。     

Hemodynamic effects of high-frequency jet ventilation in dogs with a chronically banded pulmonary artery

Two to seven weeks after banding the main pulmonary artery, the hemodynamic effects of high-frequency jet ventilation (HFJV) and conventional mechanical ventilation (CMV) were studied in dogs with and without PEEP. In comparison with CMV, HFJV significantly increased cardiac index, stroke index (SI), left ventricular stroke work index, and oxygen delivery index, and decreased pulmonary vascular resistance index both with and without PEEP; however, there were significant decreases in PaO2 and increases in intrapulmonary physiologic shunt ratio in HFJV without PEEP. SI without PEEP was significantly greater with HFJV when the peak airway pressure was synchronized with the diastole in pulmonary arterial pressure (PAP) than with CMV and with HFJV synchronized with the systole in PAP. These findings suggest that HFJV has hemodynamic advantages over CMV in dogs with chronically banded pulmonary artery and dilated right ventricle.     

Assessment of cardiac preload and left ventricular function under increasing levels of positive end-expiratory pressure

Objective (1) To assess the impact of high intrathoracic pressure on left ventricular volume and function. (2) To test the hypothesis that right ventricular end-diastolic volume (RVEDV) and intrathoracic blood volume (ITBV) represent cardiac preload and are superior to central venous pressure (CVP) or pulmonary capillary wedge pressure (PCWP). The validity of these parameters was tested by means of correlation with left ventricular end-diastolic volume (LVEDV), the true cardiac preload.Design Prospective animal study.Subjects Fifteen adult sheep.Interventions All animals were studied before and after saline washout-induced lung injury, undergoing volume-controlled ventilation with increasing levels of PEEP (0, 7, 14 and 21 cmH₂O, respectively).Measurements and main results Left ventricular ejection fraction (LVEF), stroke volume (LVSV) and LVEDV were measured using computed tomography. ITBV and RVEDV were obtained by the thermal dye dilution technique. At PEEP 21 cmH₂O, LVSV significantly decreased compared to baseline, PEEP 0 and PEEP 7 cmH₂O. LVEDV was maintained except for the highest level of PEEP, while LVEF remained unchanged. RVEDV and RVEF also remained unchanged. The overall correlation of RVEDV and ITBV with LVEDV was satisfactory (r=0.56 and r=0.62, respectively) and clearly superior to cardiac filling pressures.Conclusion In the present study, (1) ventilation with increasing levels of PEEP did not alter RV function, while LV function was impaired at the highest level of PEEP; (2) unlike cardiac filling pressures, ITBV and RVEDV both provide valid estimates of cardiac preload even at high intrathoracic pressures.This study was supported by a grant from the Faculty of Clinical Medicine, University of Mannheim.     

不同呼气末正压设定对机械通气患者血流动力学及心功能的影响

目的探讨不同呼气末正压(PEEP)水平对机械通气患者血流动力学及心功能的影响。方法将39例呼吸衰竭进行机械通气的危重患者根据心排血指数(CI)分为两组。应用部分CO2重复呼吸法(NICO)连续监测血流动力学,观察心功能正常组(CI≥2.0L.min-1.m-2,n=18)与心功能低下组(CI<2.0L.min-1.m-2,n=21)在双水平气道正压通气(BIPAP)模式下0、5、7、10和13cmH2O(1cmH2O=0.133kPa)PEEP水平对血流动力学心排血量(CO)、CI、肺毛细血管血流(PCBF)、中心静脉压(CVP)、外周血管阻力(SVR)、肺机械参数内源性呼气末正压(PEEPi)、气道峰压(PIP)、平均气道压(Pmean)及脉搏血氧饱和度(SpO2)、血压(BP)、心率(HR)等的变化。结果心功能正常组随PEEP增加,CVP明显升高,CO、CI、SVR和PCBF无明显变化;心功能低下组随PEEP增加,CVP明显升高,CO、CI呈曲线变化,且明显下降,SVR下降后显著升高,PCBF明显减少;两组患者随PEEP增加,Pmean、PIP、PEEPi均相应增加,气道阻力明显下降。结论机械通气在相对容量恒定时,在0~13cmH2O的PEEP对正常心脏无明显影响,对衰竭心脏可明显减少右心前负荷、PCBF和左心室前负荷,设定适当PEEP可改善心功能。气道压力的变化与CO、CI的变化并非一致。     

Echocardiographic analysis of cardiac function during high PEEP ventilation

Objective Does positive end-expiratory pressure ventilation (PEEP) deteriorate cardiac contractilityDesign By means of echocardiography nine piglets were studies during ventilation with 0, 15 and 25 cmH₂O (PEEP). Recordings were made before and after 500ml of 6% dextran 70.Measurement and results Right and left ventricular enddiastolic diameters were plotted against the stroke volume determined by the thermodilution technique. By combining observations made before and after volume expansion during the different ventilation modes, a ventricular function curve was obtained. The slopes of the curves were similar during all three ventilation modes, both on the left and on the right side.Conclusion This study indicates undisturbed myocardial contractility during PEEP ventilation. We infer that the cardiac output deterioration in the intact animal is caused entirely by impairment of venous return.     

呼气末正压对机械通气患者上腔静脉横径的影响

目的评价呼气末正压(PEEP)对机械通气患者的上腔静脉横径值(SVCD)的影响。方法受试的22例机械通气患者在不同水平PEEP(0～20 cm H_2O)时,应用多谱勒超声检查来监测其SVCD值,同时记录患者心率、平均动脉压与动脉血氧饱和度。统计学处理所有计量资料,以及SVCD与PEEP相关性分析。结果SVCD值随PEEP值增加而减少,且SVCD值的变化与PEEP值的变化呈显著性负相关(r=-0.981。)结论机械通气时SVCD值随PEEP值增加而减少,从而可用多普勒超声心动图检查来监测SVCD值以评价患者液体治疗效果。     

Determination of cardiac output during positive end-expiratory pressure--noninvasive electrical bioimpedance compared with standard thermodilution

Many investigators have demonstrated the accuracy and reliability of thoracic electrical bioimpedance (TEB) in spontaneously breathing patients and under mechanical intermittent positive-pressure ventilation. Most of these studies showed a good correlation between TEB and invasive methods, such as thermodilution (TD) or the Fick method. But during PEEP, contrary results occur when comparing TEB and TD. In six patients undergoing neurosurgical interventions, TEB cardiac output measurements were compared during zero end-expiratory pressure (ZEEP) and during PEEP at 8 cm H2O with a low respiratory rate. The data revealed a good correlation during ZEEP (r = .93) and during PEEP (r = .91). There was no significant statistical difference when measuring cardiac output by TEB during ventilation with PEEP. During normal or decreased cardiac output, TEB overestimated cardiac output compared with TD, whereas TEB underestimated cardiac output compared with TD during increased cardiac output, especially during PEEP.     

应用超声心动技术分析机械通气对左室功能的影响

目的 应用超声心动技术评价机械通气时呼气末正压(PEEP)对左室功能的影响.方法 将36例呼吸衰竭行机械通气的危重患者按心排血指数(CI)分为两组.应用彩色超声心动技术检测患者不同PEEP(0、4、7、10、14 cm H2O,1 cm H2O=0.098 kPa)时左室功能.结果 心功能正常组(CI≥2.0 L·min-1·m-2,17例)随PEEP增加,代表左室收缩功能的指标左室收缩期末容积(LVESV)、左室舒张期末容积(LVEDV)、心排血量(CO)、射血分数(EF)未见明显变化,代表左室舒张功能的指标二尖瓣口舒张早期充盈速度(E)、舒张晚期充盈速度(A)、E/A比值、舒张早期运动速度(Ve)、舒张晚期运动速度(Va)、Ve/Va比值及左室舒张期末压(LVEDP)未见明显改变.心功能异常组(CI＜2.0 L·min-1·m-2,19例)随PEEP增加到10 cm H2O和14 cm H2O时,与PEEP 0比较,左室收缩功能指标LVESV(ml:10 cm H2O时21.2±1.2比18.2±1.4)明显升高,LVEDV(ml:42.6±2.4、40.1±1.9比44.5±3.5)、CO(L:2.3±0.6、2.1±0.7比2.6±0.7)、EF(0.40±0.02、0.39±0.02比0.42±0.02)明显下降(均P＜0.05);左室舒张功能指标A(cm/s:88.5±15.2、93.2±18.7比76.0±9.0)、Va(cm/s:14.3±4.5、15.8±5.3比12.0±1.2)、LVEDP[mm Hg(1 mm Hg=0.133 kPa):15.3±2.0、16.9±2.8比10.7±2.5]明显升高,E(cm/s:73.6±15.4、63.2±16.4比83.1±20.1)、E/A比值(0.83±0.10、0.68±0.20比1.10±0.20)、Ve(cm/s:11.7±1.8、10.4±2.0比13.8±2.8)、Ve/Va比值(0.8±0.1、0.6±0.2比1.2±0.2)明显下降(均P＜0.05).结论 与机械通气时,0～14 cm H2O的PEEP对正常心脏无明显影响;心功能低下患者,当PEEP≥10 cm H20时可明显降低左室舒张和收缩功能;设定最佳PEEP可改善左室功能.

Abstract：

Objective To study the effects of different positive end-expiratory pressure (PEEP) levels on the heart function of patients undergoing mechanical ventilation (MV) with echocardiography. Methods Thirty-six critical patients with respiratory failure undergoing MVwere divided into two groups according to the cardiac index (CI). The left heart function was measured with echocardiography at different PEEP levels (0, 4, 7, 10, 14 cm H2O, 1cm H2O = 0. 098 kPa). Results In the normal cardiac function group (CI≥2. 0 L · min-1 · m-2, n=17), an increase in PEEP had no significant effects on left ventricular systolic function [left ventricular end-systolic volume (LVESV), left ventricular end-diastolic volume (LVEDV),cardiac output (CO), ejection fraction (EF)]. The increase in PEEP had no significant effect on left ventricular diastolic function [mitral early diastolic filling velocity (E), late diastolic filling velocity (A), the ratio of E/A, early diastolic velocity (Ve), late diastolic velocity (Va), the ratio of Ve/Va, left ventricular end-diastolic pressure (LVEDP)]. In the poor cardiac function group (CI＜ 2. 0 L · min-1 · m-2, n = 19),when PEEP was increased to 10 cm H2O and 14 cm H2O, compared with PEEP 0, left ventricular systolic function indexes including LVFSV (ml: 21.2±1.2 vs. 18. 2±1.4 as 10 cm H2O) was significantly higher,i.e. LVEDV (ml: 42. 6±2. 4, 40. 1±1.9 vs. 44. 5±3. 5), CO (L: 2. 3±0. 6, 2. 1±0. 7 vs. 2. 6±0. 7), EF (0. 40±0. 02, 0. 39±0. 02 vs. 0. 420. 02) were decreased (all P＜0. 05); left ventricular diastolic function indexes including A (cm/s: 88.5±15.2, 93.2±18.7 vs. 76.0±9.0), Va (cm/s: 14.3±4.5, 15.8±5.3vs. 12.0±1.2), LVEDP [mmHg (1 mm Hg=0.133 kPa):15.3±2.0, 16.9±2.8 vs. 10.7±2.5] were significantly higher; E (cm/s: 73. 6±15.4, 63.2±16.4 vs. 83.1±20.1), the ratio of E/A (0. 83±0. 10,0.68±0.20 vs. 1.10±0.20), Ve (cm/s: 11.7±1.8, 10.4±2.0 vs. 13.8±2.8), the ratio of Ve/Va (0. 8±0. 1, 0. 6±0. 2 vs. 1.2±0. 2) were decreased (all P＜0. 05). Conclusion Under the same condition of MV, change in PEEP levels (0 - 14 cm H2O) do not produce any obvious effect in the normal cardiac function group, on the other hand when PEEP≥10 cm H2O left heart function is significantly dowered in the poor cardiac function group. Optimial PEEP may improve the cardiac function.     

Changes of right ventricular function with positive end-expiratory pressure (PEEP) in man

The side effects of positive pressure ventilation on cardiovascular function are well known. However, in most clinical studies its influence on left ventricular function was examined. In the present study right ventricular (RV) performance was studied in 13 patients undergoing coronary artery bypass grafting during mechanical ventilation with and without positive end-expiratory pressure (PEEP). In the majority of patients (10/13), PEEP caused a decrease in RV end-diastolic volume (by 18%) whereas RV ejection fraction did not change. In the remaining 3 patients, end-diastolic and end-systolic RV volumes increased by 25% and 50% respectively and ejection fraction decreased by 29%. These results suggest that PEEP can affect RV function in two different ways: first, in the majority of patients studied, PEEP exerted an unloading effect on the RV whereas second, in 3 patients RV dilatation and a decrease in ejection fraction was observed.